A Hubble Space telescope census reveals that
black holes are common in galaxies, according to a January 13 release on the
Internet. Three black holes have been identified in three normal galaxies, and
the team responsible suggests that nearly all galaxies may harbour supermassive
black holes which once powered quasars which are now no longer active.

They took a census of 27 nearby galaxies with
NASA's Hubble Space telescope and the ground-based Canada-France-Hawaii
telescope (CFHT) on Mauna Kea, Hawaii, which are being used to conduct a
spectroscopic and photometric survey of galaxies to find black holes which have
consumed the mass of millions of sun-like stars.

The key results are that:

Supermassive black holes are so common that
nearly every large galaxy has one.

A black hole's mass is proportional to the
mass of the host galaxy, so a galaxy twice as massive as another would have a
black hole that is also twice as massive. This discovery suggests that the
growth of the black hole is linked to the formation of the galaxy in which it
is located.

The number and masses of the black holes found
are consistent with what would have been required to power the quasars.

Two of the black holes weigh 50 million and
100 million solar masses, and they lie in the cores of galaxies NGC 3379 (also
known as M105) and NGC 3377 respectively. These galaxies are both in the
"Leo Spur," a nearby group of galaxies about 32 million light-years
away and roughly in the direction of the Virgo cluster. Some 50 million
light-years away, also in the Virgo cluster, NGC 4486B has a
500-million-solar-mass black hole. It is a small satellite of the very bright
galaxy, M87 in the Virgo cluster. M87 has an active nucleus and is known to
have a black hole of about two billion solar masses.

These new results suggest that smaller
galaxies probably have lower-mass black holes, below Hubble's detection limit.
The survey shows the black hole's mass is proportional to the host galaxy's
mass. Now cosmologists will need to work on explaining why the black holes are
so common, and why they seem to be proportional to the masses of the home
galaxies.

The Hubble telescope's high resolution allowed
the team to measure the velocities of stars orbiting the black hole. A sharp
rise in velocity means that a great deal of matter is locked away in the
galaxy's core, creating a powerful gravitational field that accelerates nearby
stars.

The February 1997 servicing mission to the
Hubble telescope will involve installing the Space telescope Imaging
Spectrograph. This spectrograph will greatly increase the efficiency of
projects, such as this black hole census, that require spectra of several
nearby positions in a single object.

And in yet another galaxy . . .

The nucleus of the spiral galaxy NGC 1068 has
always been obscured from direct observation by gas and dust. But radio images
now suggest that it conceals a black hole of 10 to 20 million solar masses, and
that the gas around it is swirling into the hole so rapidly that the nucleus is
radiating at close to the theoretical limit, according to a report in Nature in
early January, by Mitchell C. Begelman and Joss Bland-Hawthorn. Black holes, it
seems, are all the go .